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Optimisation of a residential energy system with an embedded PV source

Nieuwoudt, Tielman (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The economic viability of PhotoVoltaic (PV) systems for the residential sector remains one of the greatest barriers to PV adoption. Economic viability of PV systems can be expressed in terms of a wide array of financial indicators. The economic viability of a PV system can be difficult to interpret for potential PV system owners, due to the fact that financial indicators for PV systems can involve concepts such as inflation, changing electricity tariffs, time-of-use tariffs and feed-in tariffs. This project focuses on simple payback time and determines the effect of tariff structures, load schedule optimisation and battery storage on the payback time of PV systems. The project goes on to determine whether an optimal PV system rating exists for which the payback time is minimum.
For this purpose, a mathematical model is developed for a residential energy system. This mathematical model includes the subsystems present in a smart residential energy system, namely the non-controllable loads, controllable loads, battery storage, a PV system and the grid. The grid is associated with electricity tariffs, allowing for time-of-use tariffs as well as feed-in tariffs. The mathematical model can model the energy flow between subsystems. It provides a method of calculating energy cost for the residential energy system.
A software application that implements the above mathematical model is developed to explore the payback time of residential PV systems. The application takes as input a load profile, solar profile and grid connection tariff structure. It calculates the PV system payback time as a function of PV systems rating. An optimisation is implemented to identify the PV system rating with the minimum payback time.
Financial performance and optimisation results are presented for two sets of case studies. The first set of case studies is exploratory. Using simple input parameters, cause-and-effect relationships between input parameters and results established. The second set of case studies use representative input parameters to confirm that the observed cause-and-effect relationships are present in practical residential energy systems.
The project identifies important mathematical factors that determine PV system payback time depending on the use of tariff structure, the inclusion of load schedule optimisation and/or the inclusion of battery storage. It is concluded that for each residential energy system, an optimal PV system rating with a minimum payback time exists.

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